Ignitor



G. LEWlN IGNI'I'OR Nov. 2, 1954 Filed May 28, 1952 NTOR BY; 2 2 ATTORNEUnited States Patent .n I a.

IGNITOR Gerhard Lewin, Maplewood, N. 1., assignor to WestinghouseElectric Corporation, East Pittsburgh, Pa., a corporation ofPennsylvania Application May 28, 1952, Serial No. 290,589

6 Claims. (Cl. 313-355) This invention relates to ignitor andparticularly to ignitors for use in mercury-pool ignitrons.

In general there are two types of ignitors known, of which one iscoreless and the other provided with. a core which extends well belowthe mercury surface. The ignitor dips into the mercury pool, and wherethe pool level changes, as by vaporization of part of the mercury duringuse, or by tilting of the ignitron, the resistance lengthwise of thecoreless ignitor is a variable. The purpose of the ignitor beingprovided with a core is to avoid this variation of longitudinalresistance under the differing conditons of use and attendant waste ofenergy above the mercury surface. A disadvantage of such an ignitor witha core is that the current density is uniform over the whole immersedportion of the ignitor rather than being concentrated at the mercurysurface or meniscus. Much current is therefore wasted and high currentsare required to instigate the arc.

According to the present invention, a principal feature is to have theconductive advantage of a core in an ignitor and at the same time obtaina concentration of current at the mercury surface.

More specifically, the invention contemplates an ignitor with a corehaving a relationship such that at any level, within the operatingrange, of mercury around the core, the conductivity to the core will begreatest at the level of the mercury surface.

Other objects of the invention will appear to persons skilled in the artto which it appertains, both by direct recitation thereof and byimplication from the context as the description proceeds.

Referring to the accompanying drawing in which like numerals ofreference indicate similar parts throughout the several views:

Figure l is a vertical sectional view of an ignitron showing my improvedignitor in elevation therein;

Figure 2 is a longitudinal sectional view of my ignitor in the formdisclosed in Fig. 1; and

Figures 3 and 4 are similar longitudinal sectional views of modifiedforms of ignitors embodying the invention.

Giving attention initially to the general ignitron construction ofFigure 1, arbitrarily selected for illustrative purposes, there isprovided a cylindrical casing of steel or other sturdy material having abottom 12 integral therewith and a header 13 sealed at the upper rim ofsaid casing to provide a closed envelope adapted to be evacuated.

The header provides appropriate lead-in seals 14, 15 for electrode leads16, 17 respectively for an anode 18 and ignitor 19 within the casing.The lead-in seals each include a glass or other insulating sleeve 20 bywhich the leads are kept electrically distinct from each other and fromthe casing. The anode 18 is located toward the top of the casing, wellabove the bottom wall 12, whereas the ignitor 19 is located below theanode and is directed toward and terminates at its bottom in thevicinity of, but above, the bottom wall A pool of mercury or otherreconstructing cathode material 21 is provided in the bottom of thecontainer and is of sufficient normal depth for the ignitor to always bepartially immersed therein. The mercury level, however, is not always atthe same elevation on the ignitor due to various causes and in the pastthis variation of level has had its serious effects with resistiveignitors in change of firing characteristics of the ignitron andfrequently caused arcing and skipping of firing to the detriment ofsupplementary apparatus. Attempt has been heretofore made in the art toovercome this deficiency of resistive ignitors,

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by providing a conductive core, but this did not prove successful due tothe spreading out of the current path from the mercury pool to theignitor core.

In its broadest aspect, the present invention provides .a conductivecore 22 for the .ignitor, .said'core being coaxially disposed and havinga surface within the resistive body 23 and said surface and the outersurface of.

said body having a tapered relationship such that the radial distancebetween the surface increases at successive cross sections taken nearerto the lower end of thecore than at the normal level of the pool. Thisprogressive increase of radial thickness .of the resistive body to thecore may be variously accomplished, and in Figures 1 and 2 is obtainedby tapering the lower end of the core, as at 24, from the normaldiameter of the core at about the cathode surface level, to a point at adistance from the bottom of the ignitor body and well below the normalcathode surface level. The corresponding or opposite outer wall of theignitor body may be cylindrical as shown in Figs. 1 and 2, thusincreasing the current path radially of the body to the core atsuccessive levels downwardly. As current prefers the shortest path, itnow will be clear that at any location of the mercury level, within itsusual range of variation, the shortest current path will be from themercury surface or meniscus to the core. Thus, the current density isgreatest at the surface of the mercury at whatever level the mercury mayhappen to be at the moment.

Whereas Figure 1 shows the difierential of radial distances obtained bytapering the core, the same effect may be obtained by us of acylindrical core and tapering the outer surface of the ignitor bodyoutwardly toward its lower end as shown with core 22a and ignitor body23a in Figure 3.

A more pronounced progressive differential of radial current path may beobtained, if desired, by opposite tapering of the core and ignitor body,and this reversely tapered combination is shown in Figure 4 using thetapered core 22 first described and the tapered body 23a last described.

The ignitor body may be of any usual or appropriate material or mixture,of which boron, boron carbide, and boron nitride may be given asexamples. The body is integrated at its upper end with a suitable head25 of graphite or other material to which the lead-in rod 17 may besecured. The head 25 is conductive and makes good delectrical contactwith both said core and said lead in ro In any of the constructionsshown, the tapering to obtain the increase of radial current path,begins at least no lower than the maximum level of the mercury surfaceand continues downward at least as far as minimum level to which themercury may sink in use. Furthermore, the distance of the bottom of thecore from the bottom of the ignitor body is at least as great as theradial distance of the bottom of the core to the side surface of theignitor body so that, within the operating range of mercury levels, theshortest path for the current is always from the mercury surfaceradially to the core.

I claim:

1. An ignitor comprising a resistive body portion having a peripheralouter surface, and a more conductive core in said body portion said corehaving a peripheral surface, said body portion throughout its lengththat surrounds said core being in contact with said peripheral surfaceof said core, and said surfaces being separated one from the other atprogressively greater distances toward the bottom end of the ignitor,and said core having its bottom end spaced from the bottom of said bodyportion substantially the same distance as the radial spacing of thebottom of the peripheral surface of the core from the peripheral outersurface of said body portion.

2. An ignitor comprising a resistive body portion having a cylindricalouter surface, and a more conductive core in said body portion, saidcore having a tapered section within said cylindrical body portion andthereby providing a progressively increasing radial distance through thebody portion of the core at different transverse planes through saidcore from top to bottom of the said tapered section thereof.

3. An ignitor comprising a resistive body portion having a tapered outersection increasing in diameter toward the 'lowerend thereof, and a moreconductive core longitudinally and centrally disposed in said bodyportion, said body portion providing a progressively increasing radialdistance from the outer surface thereof to the core at differenttransverse planes through the core and tapered section :of the bodyportion.

4. An ignitor comprising a resistive body portion having a tapered outersection increasing in diameter toward the lower end thereof, and acylindrical core of uniform diameter longitudinally and centrallydisposed .in said body portion, said body portion providing aprogressively increasing radial distance from the outer surface thereofto the cylindrical core at difierent planes through the core and taperedsection of the body portion.

5. An ignitor comprising a resistive body portion having a tapered outersection, and a more conductive core having a section reversely taperedwith respect to and within the tapered body portion section and therebyproviding a progressively increasing radial distance from the outersurface of the tapered section of the body portion to the taperedsection of said core at difierent transverse planes through said taperedsections.

6. An ignitor comprising a resistive body portion having a tapered outersection increasing in diameter progressively to the lower end thereof,and a more conductive core having a tapered section decreasing indiameter progressively to the lower end thereof, said tapered section ofthe core being coaxially disposed within the tapered section of the bodyportion thereby providing in- (creasing radial distances from the outersurface of the tapered section of the body portion to the taperedsection of said core at different transverse planes through said taperedsections.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,358,615 Arnott Sept. 19, 1944 FOREIGN PATENTS Number CountryDate 573,550 Great Britain Nov. 26, 1945

